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Bujwid, Zdzislaw Jan (1959) Interaction of boron tribromide with certain organic compounds. Doctoral thesis, Northern Polytechnic.
The problems considered relate to the reactions of boron tribromide with alcohols, ethers, borate esters, and aromatic hydrocarbons and the results are compared with those available on corresponding boron trichloride systems.
Two new types of boron compounds i.e. dialkyl bromo boronates, BrB(OR)2, and alkyl dibromoborinates, Br2BOB, are described. These alkoxyboron bromides are shown to be generally unstable at room temperature, although at low temperature (-80°) they have finite stability. Factors affecting their stability, mode and mechanism of their decomposition are discussed.
The infrared spectra of alkoxyboron bromides were measured and the salient features are discussed.
Alkoxyboron bromides form complexes with pyridine; 2:1 pyridine-bromoboronate and 3:1 pyridine-dibromohorinate complexes are reported.
The boron tribromide systems with alcohols in absence and in presence of pyridine are described, and it is shown, that in the former case only with primary alcohols are borate esters formed, whilst in the latter case even t-alcohols afford esters.
The stoicheimetry and the approximate rate of reaction in the pyridine-boron tribromide/butan-1-ol/pyridine system are reported.
Boron tribromide is shown to be a more effective cleaving agent for ethers than boron trichloride, because in the trihalide-ether system bromoboronates are still active agents, whereas chloroboronates are not. There are also differences in the mode of fission between the two halides, notably with the di-primary alkyl ethers, when the boron tribromide fission is believed to involve 3N2 displacement, whereas the trichloride fission proceeds by a carbonium ion mechanism.
Diphenyl ether is not cleaved by the tribromide, however in this case nuclear aromatic substitution occurs. Nuclear boronation, a new aromatic electrophilic substitution reaction, takes place also with benzene, in the presence of aluminium tribromide, to afford phenylboron dibromide. This reaction may prove of value for the synthesis of arylboron compounds.
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